1. Field of the Invention
This invention relates to multi-color screen printing apparatus and more particularly to mechanizing manual screen printing apparatus heretofore used to print multi-color on workpieces, typically textile goods mounted on pallets carried on a rotatable indexer with each pallet being indexed to each of several printing stations at which a printing screen was swung downwardly by the operator who also manually moved the squeegee back and forth across the screen in print and flood strokes.
2. Description of the Prior Art
In addition to the manual apparatus disclosed in the aforesaid patent application Ser. No. 932,779, larger and more expensive screen printing apparatus is available for multi-color printing as disclosed in U.S. Pat. No. 4,099,460 and U.S. Pat. No. 4,724,760. In this latter kind of apparatus, a central turntable or in indexer has a plurality of arms each carrying a workpiece into each of a plurality of print units which are located peripherally about the indexer and which are free-standing screen printers. That is, the screen printers are standing alone and are mounted on the floor at locations radially outward of the indexer which carries a series of circumferentially spaced workpieces and intermittently shifts each workpiece into a registration position beneath the printing screen and the squeegee and flood bar of a printer unit. A motor drive lowers the print head and screen and a motor drive reciprocates the squeegee across the screen to print on the workpiece therebelow. The timing and registration of the indexer movement to the actuation of the printing units is achieved by a Geneva drive and a locking registration bar and pin arrangement which interlocks the large mass of the indexer to each print head, such indexer movement and registration is disclosed in U.S. Pat. No. 4,724,760. The printing units are very heavy and large machines having their separate motors, printing head lift mechanisms, and squeegee and flood bar actuating mechanisms. This is in contrast to the manual machine which has no printing head motor lifts and no motorized actuation of the squeegee through print and flood strokes.
The present invention is directed to mechanization of machines which were previously manually operated, but without having the stand-alone separate printing units located radially outwardly of the indexer. Because these manual machines are substantially less expensive than the stationary large stand-alone printers with their common workpiece indexer, it is desired to build a machine which costs substantially less than the machine having the larger stand-alone multi-printers and a machine which will be attractive in price to users of the manual multi-printers because of savings in labor costs due to faster printing with less manual labor. A number of problems arise in mechanization of such equipment and among these are the supporting of multiple printing heads on the indexer without making the indexer too massive or expensive and achieving an economical and simple way of supporting the heavy vertical load, balancing the units for rotation, and registering for printing at each of the print stations.